Such a vacuum cleaner, which is known from U.S. Pat. No. 5,062,870 is being used for removing dust from a surface. By means of the motor driven fan unit a flow of air will be created through the vacuum cleaner. The known vacuum cleaner is provided with a movable valve for closing off the air inlet opening at a certain differential pressure between the air inlet opening and the dust chamber. By closing off the air inlet opening dust laden air is being prevented from entering the vacuum cleaner when the dust chamber is full with dust.
In vacuum cleaners for removing dry dust it is also known to detect the current needed for driving the motor or the motor torque needed for rotating the fan unit. If the current of torque level reaches a certain predetermined level, this will be an indication that the dust chamber is full.
GB 1,400,106 discloses a suction cleaner, particularly for removing both solids and liquids from surfaces, comprises a motor-fan unit mounted on a receptacle into which it draws picked up material, e.g. via a nozzle and hose coupled to an inlet, and a filter diaphragm spaced from but extending across the admission inlet of the unit, and deflectable due to the pressure drop across it which occurs during operation of the cleaner due to partial clogging of the filter diaphragm, and/or by engagement by a member moved in response to the liquid level in the receptacle, to cause a sealing pad, supported between the filter and the inlet, to close the latter, thereby halting the pick-up of material. The filter is moved against the action of a coil spring to close the inlet by the pad, the movement of the filter being assisted, when liquid is collected, by a cranked arm acted upon by a float.